They are on their way. Bran Stowman (or however it is spelled) is going to debut soon and he's about the size of Kane and a legit strongman. And Jason Jordan will get a push, it is inevitable.
Not to mention people getting try outs.
This right here is Beast, one of the guys on the Swedish version of American Gladiators and a pro wrestler/MMA fighter. He has a try out with WWE next week in England and he's legit the height of the Undertaker.
Big guys are coming, they just take longer to develop since they more often than not come from other backgrounds than pro wrestling.